Sending station, relay station, and relay method

ABSTRACT

In a relay station, a packet fragmented by a sending station is received. The fragmented packet is selectively further fragmented into a plurality of refragmented packets. Identification information (FSN) is added to each of the refragmented packets and to a non-refragmented packet not fragmented. Each of the packets to which the identification information (FSN) has been added is transmitted to a receiving station. This makes it possible to prevent a conflict of information (FSN) between packets due to the packet refragmentation in the relay station.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation Application of a PCT internationalapplication No. PCT/JP2006/325641 filed on Dec. 22, 2006 in Japan, theentire contents of which are incorporated by reference.

TECHNICAL FIELD

The present invention relates to a sending station, a relay station, anda relay method, for example to a technique particularly suitable in thecase where, in a relay station that receives a packet fragmented andtransmitted by a sending station and retransmits (relays) it to areceiving station, the fragmented packet is further fragmented andrelayed.

BACKGROUND ART

Wireless communication systems, such as W-CDMA (Wideband Code DivisionMultiple Access) and CDMA2000 communication systems, which performcommunication through wireless communication channels have spreadworldwide. In such wireless communication systems, a plurality of radiobase stations are deployed in a service area, and a radio terminalcommunicates with another through any of the radio base stations. Inthis wireless communication, adjacent radio base stations have anoverlapping zone between their wireless communicable service areas sothat even when the wireless communication environment worsens, signalscan be handed over between the base stations.

The wireless communication method adopts code division multiplexing,time division multiplexing, frequency division multiplexing, orthogonalfrequency division multiplexing, and so forth. Therefore, multiple radioterminals are usually able to connect with one radio station at the sametime.

However, even within the wireless communicable service area of a radiobase station, it is often difficult to perform high-speed communicationin the vicinity of the area boundary because the wireless communicationenvironment is not very satisfactory. In addition, even within the area,the propagation of radio signals is disturbed by buildings, etc., sothat an insensitive zone sometimes occurs in which a satisfactory radioconnection with a radio base station is difficult.

Hence, it has been proposed that relay stations (RSs) are disposedwithin the service area of the radio base stations so that the radioterminals and radio base stations can perform wireless communication viaRSs. Particularly, in the task group of the IEEE 802.16j, theintroduction of such a relay station is now being examined.

Matters on the IEEE 802.16 are disclosed, for example, in the followingnonpatent documents:

-   Nonpatent document 1: IEEE Std 802.16-2004-   Nonpatent document 2: IEEE Std 802.16e-2005

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

According to the background art described above, a radio terminal(mobile state (MS)) can communicate with a base station (BS) directly orthrough a relay station (RS), but it is necessary to examine how theradio terminal (MS) utilizes the relay station (RS). This is becausethere is no guarantee that in the communication via RS, the radioresources, modulation methods, and the like between BS and RS are thesame as those between RS and MS.

An example is illustrated in FIG. 12. In the figure, a 1500-byte IP(Internet Protocol) packet (herein after referred as simply to a packet)is transferred from BS through RS and to MS. In this downlink (DL), BSand RS are often deployed so that they can satisfactorily communicatewith each other, so in many cases high-speed communication is possibleusing multi-valued modulation etc.

For instance, in the case where the downlink (DL) communication from BSto RS is performed using 64QAM (Quadrature Amplitude Modulation) when arate of encoding error correction codes is ½, the DL communication canbe performed with an efficiency of 3 bits/symbol. Therefore, a 1500-byteIP packet can be transmitted by 4000 symbols.

In contrast to this, since the DL communication from RS to MS is oftenNon-line-of-sight communication, the case capable of using multi-valuedmodulation is reduced compared with the DL communication from BS to RS.FIG. 12 shows the case where the modulation method is QPSK (QuadraturePhase-Shift Keying) and the encoding rate is ½, and in this case, the DLcommunication from RS to MS is done with an efficiency of 1 bit/symbol.

At this time, assuming that the radio resource of the same amount as theradio resource from BS to RS (4000 symbols) is assigned to the DLcommunication from RS to MS, RS can transmit only 500 bytes to MS. Forthat reason, for example, RS needs to fragment a 1500-byte IP packet(fragmentation), transmit a 500-byte packet to MS, and transmit theremaining 1000 bytes at the next transmission chance.

The aforementioned nonpatent document 1 defines a function offragmenting a packet. According to the nonpatent document 1, when anMAC-SDU (Service Data Unit), such as an IP packet etc., is fragmentedinto a plurality of pieces, a fragmentation subheader is added to eachfragment.

The fragmentation subheader, in fragmenting an MAC-SDU into a pluralityof MAC-SDUs and transmitting them, is used to add to each fragmented SDUa sequence number and control bits (FC: Fragmentation Control) thatindicates which part (location) of the original packet the fragmentedSDU belongs to. Note that an MAC-SDU (IP packet etc.) to which a GMH(Generic MAC header) and a fragmentation subheader have been added isreferred to as an MAC-PDU.

FIG. 13 illustrates a typical example of the fragmentation. In thefigure, as illustrated in (1), a certain MAC-ADU (sic) #1 is fragmentedinto a first MAC-SDU #1-1 and a second MAC-SDU #1-2, and a GMH and afragmentation subheader (indicated by the shaded portion) are added toeach fragment, whereby two MAC-PDUs are formed. In (2), a GMH and asubheader are added to an MAC-SDU #2 not fragmented, whereby one MAC-PDUis formed. Although not illustrated in FIG. 13, a CRC (Cyclic RedundancyCheck) error-checking code may be added to the MAC-PDU to detect anerror.

As to the format of the fragmentation subheader, for example, in thecase where an ARQ (Automatic Repeat Request) is disabled, two followingpatterns are prepared according to connection type:

(a) ARQ-disabled and Extended-Type Connection

(b) ARQ-disabled and non-Extended-Type Connection

The two patterns are illustrated in FIGS. 14( a) and 14(b),respectively. The former pattern, as illustrated in FIG. 14( a), has anFC (Fragmentation Control) field (two bits), an FSN (Fragment SequenceNumber) field (11 bits) in which a sequence number is added to eachfragmented MAC-SDU, and a reserved field (3 bits). The latter format, asillustrated in FIG. 14( b), has an FC field (2 bits), an FSN field (3bits), and a reserved field (3 bits).

Each field in the fragmentation subheader format is explained in thefollowing Table 1.

TABLE 1 Fragmentation Subheader Format Field name Description FC 00: Nofragment 01: Last fragment 10: First fragment 11: Middle fragment FSNThe sequence number of SDU fragment

The FC field is a fragmentation control bit representing the location ofa fragment. As illustrated in Table 1, FC=00 represents that thisMAC-SDU is not a fragment, FC=01 represents the last fragment of thefragmented MAC-SDUs, FC=10 represents the first fragment of thefragmented MAC-SDUs, and FC=11 represents the middle fragment of thefragmented MAC-SDUs. The FSN field represents a sequence number that isincremented one by one in a series of fragmented MAC-SDUs.

Therefore, when the MAC-SDU fragmented in BS is further fragmented inRS, a conflict is caused between FSNs, and consequently, the MAC-PDU cannot be reconstructed accurately from the fragemented MAC-SDUs at thereceiving side. An example of the conflict is illustrated in FIG. 15. Inthe case where in BS a certain MAC-SDU is fragmented into two and FSN=1and FSN=2 are respectively added to the two, for example, when in RS thefragmented MAC-SDU with FSN=1 is further fragmented into two, FSN=1 andFSN=2 are sometimes added to the two. In such a case, in RS, a conflicttakes place between FSN=2, which has been added to the MAC-SDUfragmented in BS but not fragmented in RS, and FSN=2, which has beenadded to the MAC-SDU fragmented in both BS and RS.

The present invention has been made in view of the problems describedabove. Accordingly, an object of the present invention is to prevent theoccurrence of a conflict between FSNs that is caused by furtherfragmentation of a received packet (fragmented packet) in a relaystation.

Still another of this invention is to facilitate a packet fragmentationprocess in a relay station and implement the fragmentation and relay ofa packet capable of preventing the above-described conflict andmismatch, by packing packets that were fragmented beforehand into blockswhich are used as a unit of fragmentation in the relay station, and thentransmitting the packed packet to the relay station.

A further object of this invention is to make further utilization ofradio resources possible by reducing the size of the packed packet thatis transmitted to the relay station.

It is noted that accomplishing advantageous effects that are derivedfrom the following preferred embodiments of the present invention butnot obtained by prior art, in addition to the above objects, can also bepositioned as one of other objects of the invention.

Means for Solving the Problems

To achieve the above objects, the important features of the presentinvention reside in the following systems and methods.

(1) A first aspect of the relay station of the present invention is arelay station for receiving a packet transmitted from a sending stationand relaying the packet to a receiving station. The relay stationcomprises a packet receiver configured to receive a packet fragmented inthe sending station; a packet fragmenting unit configured to selectivelyfurther refragment the packet received by the packet receiver into aplurality of refragmented packets; a controller configured to addidentification information to each of the refragmented packets and to apacket not refragmented in the packet fragmenting unit; and a packettransmitting unit configured to transmit to the receiving station eachof the packets to which the identification information has been added bythe controller.

(2) In the first aspect of the relay station, the packet fragmentingunit may include a fragmentation determiner that, based on apredetermined reference, determining whether the packet received by thepacket receiver is further fragmented into the plurality of refragmentedpackets; and a packet refragmenting unit that refragments the fragmentedpacket if the fragmentation determiner determines that the fragmentedpacket is further fragmented.

(3) In addition, if a packet size of the fragmented packet received bythe packet receiver exceeds a size that is transmittable to thereceiving station at that time, the fragmentation determiner maydetermine that the fragmented packet is further fragmented.

(4) The controller may include a sequence number assigner for adding asequence number to the refragmented packet and the non-refragmentedpacket as the identification information regardless of therefragmentation.

(5) The controller may further include a sequence number manager formanaging the sequence number according to a connection with thereceiving station, and the sequence number assigner may add the sequencenumber to the refragmented packet and non-refragmented packet of thesame connection under management of the sequence number manager.

(6) A second aspect of the relay station of the present invention is arelay station for receiving a packet transmitted from a sending stationand relaying the packet to a receiving station. The relay stationcomprises a packet receiver configured to receive a fragmented packetwhich contains a fragment of the packet fragmented in the sendingstation, and also contains control information representing which partof the packet the fragment belongs to before fragmentation; a packetfragmenting unit configured to selectively further refragment the packetreceived by the packet receiver into a plurality of refragmentedpackets; a controller configured to add to the refragmented packetsrenewed control information which matches with the control informationadded before the refragmentation, based on the control information; anda packet transmitting unit configured to transmit the refragmentedpackets to which the renewed control information has been added, and thepacket not refragmented by the packet fragmenting unit, to the receivingstation.

(7) In the second aspect of the relay station, the second informationmay contain information representing any one of four states:nonfragmentation, first packet, middle packet, and last packet.

(8) In addition, if the control information contained in the fragmentedpacket received by the packet receiver represents a first packet, thecontroller may add control information representing a first packet toone of the refragmented packets and control information representing amiddle packet to the other. If the control information contained in thefragmented packet represents a middle packet, the controller may addinformation representing a middle packet to each of the refragmentedpackets. If the control information contained in the fragmented packetrepresents a last packet, the controller may add control informationrepresenting a last packet to one of the refragmented packets andcontrol information representing a middle packet to the other.

(9) A first aspect of the sending station of the present invention is asending station for transmitting a packet to a relay station thatreceives the packet and relays the packet to a receiving station. Thesending station includes a packet fragmenting unit configured tofragment a packet into a plurality of blocks that are used as a unit offragmentation in the relay station; a controller configured to addidentification information to each of the blocks fragmented by thepacket fragmenting unit; a packet packing unit configured to pack someof the blocks to which the identification information has been added;and a packet transmitting unit configured to transmit the packets packedby the packet packing unit to the relay station.

(10) In the first aspect of the sending station, it may further includea header assigner for adding header information to the packets packed bythe packet packing unit.

(11) In addition, the identification information may be a sequencenumber that is incremented one by one in the blocks.

(12) Furthermore, the packet packing unit may pack blocks that are thesame in a connection with the receiving station.

(13) A third aspect of the relay station of the present invention is arelay station for receiving a packet transmitted by a sending stationand relaying the packet to a receiving station. The relay stationincludes a packet receiver for receiving as a packet a plurality ofblocks fragmented in the sending station which have been assignedidentification information respectively, packed into one, andtransmitted by the sending station; a packet fragmenting unit which, ifit is necessary to fragment and transmit the packet received by thepacket receiver to the receiving station, separates the packet into theplurality of blocks to generate a plurality of fragmented packets; and apacket transmitting unit configured to transmit to the receiving stationthe plurality of fragmented packets generated by the packet fragmentingunit.

(14) In the third aspect of the relay station, the identificationinformation may be a sequence number that is incremented one by one inthe blocks.

(15) A first aspect of the relay method of the present invention is arelay method for use in a relay station that receives a packettransmitted from a sending station and relays the packet to a receivingstation. The relay method comprises the steps of receiving a packetfragmented in the sending station; selectively further fragmenting thefragmented packet into a plurality of refragmented packets; addingidentification information to each of the refragmented packets and to anon-refragmented packet not fragmented; and transmitting to thereceiving station each of the packets to which the identificationinformation has been added.

(16) A second aspect of the relay method of the present invention is arelay method for use in a relay station that receives a packettransmitted from a sending station and relays the packet to a receivingstation. The relay method comprises the steps of receiving a fragmentedpacket which contains a fragment of the packet fragmented in the sendingstation, and also contains control information representing which partof the packet the fragment belongs to before fragmentation; selectivelyfurther refragmenting the fragmented packet into a plurality ofrefragmented packets; adding to the refragmented packets renewed controlinformation which matches with the control information added before therefragmentation, based on the control information; and transmitting therefragmented packets to which the renewed control information has beenadded, and a packet not refragmented, to the receiving station.

(17) A third aspect of the relay method of the present invention is arelay method for a relay station to receive a packet transmitted from asending station and relay the packet to a receiving station. The sendingstation fragments a packet into a plurality of blocks that are used as aunit of fragmentation in the relay station; adds identificationinformation to each of the plurality of blocks; packs some of the blocksto which the identification information has been added; and transmitsthe packed packet to the relay station. The relay station receives thepacket from the sending station; if it is necessary to fragment andtransmit the received packet to the receiving station, separates thepacket into the plurality of blocks to generate a plurality offragmented packets; and transmits the plurality of fragmented packets tothe receiving station.

Advantages of the Invention

The present invention possesses the following effects and advantages:

(1) The conflict of information (such as FSN etc.) and mismatch ofcontrol information between a fragmented packet and a nonfragmentedpacket resulting from further packet fragmentation in the relay stationcan be prevented, so the relay station can perform flexible packetfragmentation and relay according to radio resources such as radio bandswhich can be utilized between itself and the receiving station. Thus, itbecomes possible to utilize radio resources.

(2) In the sending station, by fragmenting a packet beforehand into aplurality of blocks that are used as a unit of further fragmentation inthe relay station, adding identification information, such as FSN etc.,to each block and packing and sending these blocks to the relay station,the relay station is able to separate the received packet into theblocks without managing FSN and control information. Consequently, withthe above-described conflict of information and mismatch of controlinformation being prevented, it becomes possible to perform packetfragmentation and relay according to radio resources between the relaystation and the receiving station.

(3) By adding header information to the aforementioned packet afterbeing packed, the header information can greatly be reduced comparedwith the case of adding header information to each block describedabove, so further utilization of radio resources becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a wireless communication systemconfigured in accordance with a first embodiment of the presentinvention;

FIG. 2 is a block diagram illustrating the configuration of a PDUreconstructor in the relay station (RS) illustrated in FIG. 1;

FIG. 3 is a flowchart used for explaining operation of the RSillustrated in FIGS. 1 and 2;

FIG. 4 is a packet format diagram used for explaining the packing ofpackets according to a second embodiment of the present invention;

FIGS. 5( a) and 5(b) are diagrams illustrating format examples of thesubheader (packing subheader) used in the packing format illustrated inFIG. 4;

FIG. 6 is a block diagram illustrating a wireless communication systemconfigured in accordance with the second embodiment;

FIG. 7 is a block diagram illustrating the configuration of a PDUgenerator in the base station (BS) illustrated in FIG. 6;

FIG. 8 is a block diagram illustrating the configuration of the relaystation (RS) illustrated in FIG. 6;

FIG. 9 is a block diagram illustrating the configuration of a PDUreconstructor in the relay station (RS) illustrated in FIG. 8;

FIG. 10 is a flowchart used for explaining operation of the BSillustrated in FIGS. 6 and 7;

FIG. 11 is a flowchart used for explaining operation of the RSillustrated in FIGS. 6, 8, and 9;

FIG. 12 is a diagram used to explain the necessity of packetfragmentation in the relay station (RS);

FIG. 13 is a packet format diagram used to explain an example of thepacket fragmentation;

FIGS. 14( a) and 14(b) are diagrams illustrating format examples of thesubheader (fragmentation subheader) used in the packet formatillustrated in FIG. 13; and

FIG. 15 is a diagram used to explain a problem caused by fragmentationin a relay station.

DESCRIPTION OF REFERENCE NUMERALS 10 Base station (BS: sending station)101 Network (NW) interface 102 Packet identifier 103 Packet buffer 104PDU generator 141 Fragmentation/packing determiner 142 SDU fragmentingunit 143 FSN/FC assigner 144 SDU buffer 145 Header assigner 105 FSNmanagement table storage unit 106 Transmission controller 107 Encoder108 Modulator 109 Transmitter 110 Duplexer 111 Transmitter-receiverantenna 112 Receiver 113 Demodulator 114 Decoder 115 SDU regenerator 20Relay station (RS) 201 PDU buffer 202, 214 PDU reconstructor 221 PDUlength determiner 222, 226 SDU extractor 223 SDU fragmenting unit 224PDU generator 225 FSN assigner 227 Packed-SDU fragmenting unit 228Header assigner 229 Selector 203 FSN management table storage unit 204Transmission controller 205 Encoder 206 Modulator 207 Transmitter 208Duplexer 209 Transmitter-receiver antenna 210 Receiver 211 Demodulator212 Decoder 213 PDU receiver 30 Mobile station (MS: receiving station)

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described herein after withreference to the drawings. However, the invention is not to be limitedto the following embodiments. Obviously further modifications can beimplemented without departing from the scope of the invention upon thereading and understanding of this specification. All such modificationsare intended to be included within the scope of the invention.

[A] Summarized Description

To solve the above-described problems, embodiments of the presentinvention adopt the following schemes described in (1) and (2):

(1) A relay station (RS), in further fragmenting a packet alreadyfragmented, assigns a new FSN (Fragment Sequence Number) to the packetfurther fragmented.

(2) Alternatively, a packet sending station (e.g., a radio base station)fragments a packet into small blocks beforehand, and adds a sequencenumber to each block beforehand. In addition, in order to reduce theoverhead, the fragmented blocks are packed and transferred. When furtherfragmentation is needed in the relay station (RS), the packed packet isseparated into the blocks fragmented in the sending station. Becauseeach block already has its sequence number, the relay station (RS) doesnot need to add a new sequence number.

A specific example of the former (1) will herein after be described indetail as a first embodiment, while a specific example of the latter (2)will herein after be described in detail as a second embodiment.

[B] Description of First Embodiment

FIG. 1 is a block diagram illustrating a wireless communication systemaccording to a first embodiment of the present invention. The systemillustrated in the figure is equipped with a radio base station (BS) 10,a radio terminal (mobile station (MS)) 30, and a relay station (RS) 20deployed between the BS 10 and the MS 30 to relay the transmission ofinformation between the BS 10 and the MS 30. The MS 30 is configuredsuch that it can communicate with the BS 10 directly or through the RS20. In the downlink communication from the BS 10 to the MS 30, the BSfunctions as a sending station and the MS 30 as a receiving station.

The RS 20, as its major functions, includes a PDU buffer 201, a PDUreconstructor 202, an FSN management table storage unit 203, atransmission controller 204, an encoder 205, a modulator 206, atransmitter 207, a duplexer 208, a transmitter-receiver antenna 209, areceiver 210, a demodulator 211, a decoder 212, and a PDU receiver 213.

The PDU buffer (packet buffer) 201 is adapted to temporarily hold apacket normally received from the BS 10 or MS 30, i.e., an MAC-PDU(sometimes simply called a PDU herein after) until the next transmissionchance.

The PDU reconstructor (packet fragmenting unit) 202, under control ofthe transmission controller 204, is adapted to determine whether tofragment the MAC-SDU (sometimes simply called a SDU herein after) of anMAC-PDU transferred from the PDU buffer 201 on the basis of apredetermined reference (described later), selectively further fragment(refragment) the MAC-SDU according to the determination result, andreconstruct an MAC-PDU from the fragmented MAC-SDUs or a nonfragmentedMAC-SDU. In this embodiment, the PDU reconstructor 202 is equipped withthe following functions (1) and (2).

(1) First function of assigning (reassigning) a fragment sequence number(FSN) to each of the fragmented MAC-SDUs and nonfragmented MAC-SDUs thatare of the same connection irrespective of whether to fragment(refragment), based on FSNs managed according to CID (connectionidentifier) by the FSN management table storage unit 203

(2) Second function of assigning (reassigning) a new FC value (FC bits)to a fragmented MAC-SDU according to a rule described later

Owing to having these functions, the RS 20 of this embodiment is capableof preventing a conflict of FSNs from occurring between a fragmentedMAC-SDU and a nonfragmented MAC-SDU, and also capable of maintaining thematch of FC values before and after fragmentation. In other words, thePDU reconstructor 202 reassigns FSNs to a fragmented MAC-SDU and anonfragmented MAC-SDU as identification information, and also reassignscontrol information that indicates which part of the original packet afragment of the packet (fragmented in the BS 10) belongs to, with theFC-value match being maintained.

The FSN management table storage unit (sequence number manager) 203, forexample, as illustrated in the following Table 2, is adapted to storeand manage in memory (not illustrated) an FSN (Next FSN) that is nextadded to an MAC-SDU, in the form of table data (FSN management table),according to the connection identifier (CID) belonging to an MAC-PDU tobe transmitted. Note that the “Next FSN” is updated by being incrementedby 1 every time an FSN is added to an MAC-SDU.

TABLE 2 FSN Management Table CID Next FSN #1  0 #2 31 . . . . . . #N 23

The transmission controller 204 is adapted to control a PDUreconstruction process (fragmentation of SDU, addition of FSN, additionof FC, and so on) that is carried out in the PDU reconstructor 202. AtPDU transmission timing, the controller 204 is adapted to extract a PDUfrom the PDU buffer 201 and transfer it to the PDU reconstructor 202.The PDU transmission timing is decided by a scheduler (not illustrated)of the RS 20 (transmission controller 204) so that QoS (Quality ofService) is guaranteed, or the PDU transmission timing in the RS 20 isdecided by the BS 10. Based on the transmission timing information, thePDU transmission timing can be decided.

In addition, the transmission controller 204 is adapted to trigger thePDU reconstructor 202 with respect to the transmission of PDUs, and alsohas a function of specifying a transmittable PDU length or number ofbytes. A data quantity, such as a PDU length or number of bytes, whichis transmittable (transmittable size) can be decided based on availableradio resources (the number of subchannels, number of symbols, andsuch), and on the modulation method and encoding rate being used.Therefore, in systems adopting adaptive coding modulation, a dataquantity, such as a PDU length or number of bytes, which istransmittable can also be adaptively decided based on feedbackinformation on the radio reception quality from the MS 30 such as CQI,CINR, or the like.

The encoder 205 is used for adding to the PDU from the PDU reconstructor202 the required error correction codes such as turbo codes etc. Themodulator 206 is used for modulating the coded data from the encoder 205by employing the required modulation method such as QPSK, 16QAM, or thelike. The transmitter 207 is used for performing on the modulated signalfrom the modulator 206 the required wireless transmission process thatincludes DA conversion, frequency conversion to radio frequency (RF)(up-conversion), amplification to the required transmitting power by ahigh-output amplifier, and so forth.

The duplexer 208 is used for separating an outgoing signal and anincoming signal, and is adapted to output the outgoing signal from thetransmitter 207 to the transmitter-receiver antenna 209, and output theincoming signal from the transmitter-receiver antenna 209 to thereceiver 210.

The transmitter-receiver antenna (also sometimes simply called anantenna herein after) 209 is used for radiating the outgoing signal fromthe duplexer 208 into space toward the MS 30 or BS 10, and receiving asignal radiated into space from the MS 30 or BS 10.

Thus, the above-mentioned encoder 205, modulator 206, transmitter 207,duplexer 208, and transmitter-receiver antenna 209 as a whole functionas packet transmitting unit for transmitting to the MS 30 (which is areceiving station) the fragmented SDU and nonfragmented SDU to which, asdescribed previously, new FSNs and FCs have been added in the PDUreconstructor 202.

On the other hand, the receiver 210 is used for performing the requiredwireless reception process, which includes amplification by a low noiseamplifier, frequency conversion to base band frequency(down-conversion), AD conversion, etc., on an incoming signal that isreceived by the antenna 209 and input from the duplexer 208. Thedemodulator 211 is used for demodulating the incoming signal on whichthe aforementioned wireless reception process has been performed in thereceiver 210, by a demodulation method that corresponds to themodulation method at the sending side (MS 30 or BS 10).

The decoder 212 is used for decoding the incoming signal demodulated inthe demodulator 211, by a decoding method and decoding rate thatcorrespond to the encoding method and encoding rate at theaforementioned sending side. The PDU receiver 213 has a function ofidentifying information on QoS from the decoded data sent from thedecoder 212, for example from the CID added to the GMH of the PDU, andtemporarily storing a received signal in the PDU buffer 201 according tothat information, and a function of computing a cyclic redundancy check(CRC) over the aforementioned decoded data. Note that when an error isdetected from the computation result, it is also possible for thetransmission controller 204 to perform retransmission control such asHARQ etc.

Thus, the above-mentioned antenna 209, duplexer 208, receiver 210,demodulator 211, decoder 212, and PDU receiver 213 as a whole functionas packet receiver for receiving the packet fragmented in the BS 10.

(Detailed Description of PDU Reconstructor 202)

The configuration of the above-mentioned PDU reconstructor 202 isillustrated in FIG. 2 by way of example. As illustrated in the figure,the PDU reconstructor 202, in order to implement the functionspreviously described, includes a PDU length determiner 221, an SDUextractor 222, an SDU fragmenting unit 223, a PDU generator 224, and anFSN assigner 225.

The PDU length determiner (fragmentation determiner) 221, on receivingan MAC-PDU from the PDU buffer 201 at the aforementioned PDUtransmission timing, is adapted to determine whether the MAC-PDU istransmittable without being fragmented (i.e., whether a packet size tobe transmitted exceeds a transmittable size), based on the data quantitysuch as a PDU length or number of bytes, which is transmittable(transmittable size), specified by the transmission controller 204. ThePDU length determiner 221 is adapted to transfer the PDU to the FSNassigner 225 if it is transmittable (fragmentation unnecessary) at thattime, and to the SDU extractor 222 if it is not transmittable(fragmentation necessary).

The SDU extractor 222 is used to separate the PDU, which was judged tobe “Fragmentation necessary” and transferred from the PDU lengthdeterminer 221, into the header (GMH and subheader) and the SDU storedin the payload, transfer the SDU to the SDU fragmenting unit 223, andtransfer the header to the PDU generator 224.

The SDU fragmenting unit (packet refragmenting unit) 223 is used tofragment the SDU from the SDU extractor 222 into pieces so that eachpiece becomes equal to the data quantity specified by the transmissioncontrol 204, allowing for the header being added by the PDU generator224. The fragmented SDU is transferred from the SDU fragmenting unit 223to the PDU generator 224.

The PDU generator 224 is used to add the headers (including subheaders)to the fragmented SDUs to generate (reconstruct) a plurality of PDUs.The PDUs that are transmittable are transferred to the FSN assigner 225,while the PDUs not transmittable are transferred to the PDU buffer 201.

The SDU fragmenting unit 223 also has a function of updating (replacing)the FC that is contained in the fragmentation subheader. For instance,in the case of fragmenting an SDU into two, as illustrated in thefollowing Table 3, new FC values are added to the two fragmented SDUs, afirst fragment and a subsequent fragment, according to the original FCvalue.

TABLE 3 FC Updating Pattern FC after fragmentation Original FC Firstfragment Subsequent fragment 00: No fragment 10: First fragment 01: Lastfragment 01: Last fragment 11: Middle fragment 01: Last fragment 10:First fragment 10: First fragment 11: Middle fragment 11: Middlefragment 11: Middle fragment 11: Middle fragment

More particularly, when the FC value of an SDU before being fragmentedis 00 which means “No Fragment”, the first fragment of the twofragmented SDUs is assigned FC=10 which means a first fragment, whilethe subsequent fragment is assigned FC=01 which means a last fragment.When the FC value of an SDU before being fragmented is 01 which means“Last Fragment”, the first fragment of the two fragmented SDUs isassigned FC=11 which means a middle fragment, while the subsequentfragment is assigned FC=01 which means a last fragment.

Likewise, when the FC value of an SDU before being fragmented is 10which means “First Fragment”, the first fragment of the two fragmentedSDUs is assigned FC=10 which means a first fragment, while thesubsequent fragment is assigned FC=11 which means a middle fragment.When the FC value of an SDU before being fragmented is 11 which means“Middle Fragment”, each of the two fragmented SDUs is assigned FC=11which means a middle fragment.

Note that the FC-value converting rule illustrated in Table 3 is storedin the form of a table in the SDU fragmenting unit 223, or memory notillustrated of the transmission controller 204.

Thus, the SDU fragmenting unit 223, singly or in cooperation with thetransmission controller 204, functions as controller which, based on theFC value of the original SDU before being fragmented, adds (orassigning) to a fragmented SDU a new FC value which matches the originalFC value.

By adding (or assigning) new FCs, it becomes possible to assure thematch between FC values of an SDU before and after being fragmented, sothat the receiving station (MS 30 in the downlink communication or BS 10in the uplink communication) is capable of packing and reconstructing(restoring) fragmented SDUs in right combination, based on theaforementioned FSNs and FC values. Thus, FSNs and FCs are informationthat is added according to fragmentation, and serve as information thatis used to restore the original packet.

Finally, the FSN assigner (sequence number assigner) 225 is adapted toadd an FSN to a PDU (which is to be transferred) by referring to the FSNmanagement table (see Table 2) stored on the FSN management tablestorage unit 203, increment the next FSN (“Next FSN”) of the connectionidentifier (CID) related to the PDU to update the FSN management table,add a CRC as occasion demands, and transfer the processed PDU to theencoder 205.

Thus, the above-mentioned FSN management table storage unit 203,transmission controller 204, and FSN assigner 225 as a whole function ascontroller of adding FSNs to fragmented SDUs and nonfragmented SDUs asidentification information, respectively.

(Description of Operation of RS 20)

The operation of the RS 20 of this embodiment configured as describedabove will be described in detail herein after with reference to aflowchart illustrated in FIG. 3.

In the RS 20, the transmission controller 204 checks whether atransmission data quantity D has been assigned (i.e., whether the packetfragmenting function has been effectively set) (route N of step S1). Ifit has been assigned, a PDU to be transmitted is read out from the PDUbuffer 201 at the aforementioned PDU transmission timing and transferredto the PDU reconstructor 202 (route Y of step S1 to Step S2).

In the PDU reconstructor 202, on receiving the PDU from the PDU buffer201, the PDU length determiner 221 determines, based on the specifieddata quantity D from the transmission controller 204, whether the PDU istransmittable without being fragmented (step S3).

As a consequence, if it is not transmittable (i.e., if fragmentation isnecessary) (route N of step S3), the PDU length determiner 221 transfersthe PDU to the SDU extractor 222. The SDU extractor 222 separates thePDU into the header (GMH and subheader) (where H is the size of theheader) and the SDU stored in the payload, and transfers the SDU to theSDU fragmenting unit 223 and the header to the PDU generator 224 (stepS4).

The SDU fragmenting unit 223 fragments the SDU from the SDU extractor222 into an SDU #1 corresponding to the first portion (D-H) of the SDUand the remaining SDU #2, and transfers them to the PDU generator 224.

The PDU generator 224 adds the headers (size H) to the SDU #1 and SDU #2transferred from the SDU fragmenting unit 223 and updates (or replaces)the FC bits contained in the fragmentation subheaders with new FC bitsaccording to the rule illustrated in Table 3, thereby generating(reconstructing) PDUs #1 and #2 (step S6). The PDU transmittable (e.g.,PDU #1) is transferred the FSN assigner 225, while the PDU nottransmittable (e.g., PDU #2) is transferred to the PDU buffer 21 (stepS7).

On the other hand, when it is determined in step S3 that the PDU istransmittable (“Fragmentation Unnecessary”), the PDU length determiner221 transfers that PDU to the FSN assigner 225 (route Y of step S3).

The FSN assigner 225 then adds new FSNs managed in the FSN managementtable to the fragmented PDU from the PDU generator 224 and thenonfragmented PDU from the PDU length determiner 221 (step S8), andtransfers them to the encoder 205.

In this way, the transmittable PDU of the SDU fragmented in the SDUfragmenting unit 223, or transmittable nonfragmented PDU, undergoes therequired error correction encoding process, modulation process, andwireless transmission process by passing through the encoder 205,modulator 206, and transmitter 207, and then the PDU is transmitted fromthe antenna 209 toward the receiving station (MS 3 (sic) in the downlinkcommunication) (step S9).

A signal received by the antenna 209 undergoes the required wirelessreception process, demodulation process, decoding process,CRC-computation process, and other processes by passing through theduplexer 208, receiver 210, demodulator 211, decoder 212, and PDUreceiver 213, and is temporarily held in the PDU buffer 201 until thetransmission timing that is specified by the transmission controller204.

As described supra, in accordance with the present embodiment, in the RS20, regardless of whether to fragment (refragment) a received packet,the sequence number of each packet is replaced with a new sequencenumber, so that a malfunction due to a conflict of FSNs in the MS 30 canbe prevented. Therefore, it becomes possible for the RS 20 to fragment areceived packet freely (flexibly) and transmit (relay) it to the BS 30,according to radio resources such as radio bands available between theRS 20 and the MS 30. Thus, it becomes possible to utilize radioresources.

While it has been described in the first embodiment that a new sequencenumber is added to the FSN field of a fragmentation subheader (see FIGS.14( a) and 14(b)) to avoid a conflict of FSNs, it is also possible toimplement the same FSN conflict preventing function, for example, byadding identification information such as an additional sequence numberto the reserved field (3 bits) with the received FSN field remainingunchanged.

[C] Description of Second Embodiment

It will be described in this embodiment that as to the downlinkcommunication to the MS 30 (or in the uplink communication to the BS10), in the BS 10, by previously fragmenting the SDU in a PDU into smallSDUs of size equivalent to the length of the SDU fragmented in the firstembodiment, then adding FSNs to the fragments, and packing them andtransmitting to the RS 20, the addition of new FSNs resulting fromfurther fragmentation (FSN management in the RS 20) is not needed in theRS 20.

(Description of Packing)

First of all, a description will be given of the “packing” functiondefined in the aforementioned nonpatent document 1.

According to the nonpatent document 1, packing subheaders arerespectively added to a plurality of SDUs (including fragmented SDUs),and then they are packed and assigned a single GMH (Generic MAC Header).This can reduce the overhead bits due to the single GMH, compared withthe case where GMHs are respectively added to SDUs.

The packing subheader, in transmitting a plurality of SDUs as a singlePDU, is employed to add to each SDU a sequence number, control bitsrepresenting the location of the fragment, and the SDU length. Anexample of packing is depicted in FIG. 4. In the figure, while a packingsubheader, which is illustrated by shaded area, is added to two SDUs #1and #2 respectively, a single GMH common to the two is added, whereby asingle PDU is constructed. As evident from the fact that SDUs to bepacked have a GMH in common, only SDUs of the same connection identifier(CID) can be packed into the same PDU.

As to the format of the packing subheader, as with the format of thefragmentation subheader, for instance, in the case where an ARQ(Automatic Repeat Request) is disabled, two alternative patterns areprepared according to connection type:

(a) ARQ-disabled and Extended-Type Connection

(b) ARQ-disabled and non-Extended-Type Connection

The two alternative packing subheader patterns are illustrated in FIGS.5( a) and 5(b), respectively. The former pattern, as illustrated in FIG.5A, has an FC (Fragmentation Control) field (two bits), an FSN (FragmentSequence Number) field (11 bits) in which a sequence number is added toeach fragmented MAC-SDU, and an SDU length field (11 bits) whichrepresents the length of a packed SDU (including the subheader) inbytes. On the other hand, the latter format, as illustrated in FIG. 5(b), has an FC field (2 bits), an FSN field (3 bits), an SDU length field(11 bits)

Each field in the packing subheader format is explained in the followingTable 4.

TABLE 4 Packing Subheader Format Field name Description FC(Fragment 00:No fragment Control) 01: Last fragment 10: First fragment 11: Middlefragment Length SDU length (in bytes) including packing subheaderFSN(Fragment The sequence number of SDU Sequence Number) fragment

The FC field is a fragmentation control field representing the locationof a fragmented SDU (fragment) FC=00 represents that this SDU is not afragment, FC=01 represents the last fragment of the fragmented SDUs,FC=10 represents the first fragment of the fragmented SDUs, and FC=11represents the middle fragment of the fragmented SDUs. The FSN fieldrepresents a sequence number that is incremented one by one in a seriesof fragmented SDUs. The reason why the packing header contains the FCbits is that fragmentation and packing are sometimes performed at thesame time.

As illustrated in FIGS. 5( a) and 5(b), the packing subheader furthercontains information on SDU length in addition to the fragmentationsubheader. Therefore, the sending station (BS 10 in the downlinkcommunication) fragments an SDU into small SDUs and packs them, andsends the packed SDU to the RS 20 as a single PDU. In this manner, whenit is necessary to fragment the received PDU, the fragmentation in theRS 20 is limited to the unit of the length of the SDU fragmented in theBS 10, but the addition of new sequence numbers, updating of FC bits,etc. are not needed in the RS 20, as they are done in the firstembodiment. This makes it possible to lighten the processing workload inthe RS 20.

In the following description, attention is directed to the transmissionof packets from the BS 10 to RS 20 and from RS 20 to the MS 30(downlink). Note that as to an uplink which is the inverse of adownlink, packet fragmentation and packing can be similarly implementedby the same operation as the following operation. Note also that in thefollowing description, parts given the same reference numerals as theaforementioned reference numerals denote the same parts as theaforementioned parts or corresponding parts, unless otherwise specified.

(Description of BS 10)

FIG. 6 is a block diagram illustrating the configuration of a wirelesscommunication system according to a second embodiment of the presentinvention. In the wireless communication system illustrated in FIG. 6,the BS 10 includes, as its major functions, a network (NW) interface101, a packet identifier 102, a packet buffer 103, a PDU generator 104,an FSN management table storage unit 105, a transmission controller 106,an encoder 107, a modulator 108, a transmitter 109, a duplexer 110, atransmitter-receiver antenna 111, a receiver 112, a demodulator 113, adecoder 114, and an SDU regenerator 115.

The NW interface 101 is used to interface with a higher network. Thebuffer identifier 102 is used to identify a destination (MS 30) and aQoS class based on information such as the IP header of the receivedpacket from the NW interface 101, etc., and temporarily hold thereceived packet in the packet buffer 103 according to the identifydestination (MS 30) or connection identifier (CID) which corresponds tothe QoS class.

The packet buffer 103, as described above, is used to temporarily hold areceived packet according to the CID until transmission timing that isinstructed from the transmission controller 106. The PDU generator 104is used to generate a PDU from the packets transferred from the packetbuffer 103, under control of the transmission controller 106. In thisembodiment, the PDU generator 104 is adapted to (1) determine whethertransmit the packet from the packet buffer 103 which is fragmentedand/or packed, (2) fragment the SDU into a plurality of blocks (smallSDUs) if fragmentation is necessary, and (3) pack the small SDUs afterFSNs and FCs are respectively added to them. This size of the SDUfragmented in the PDU generator 104 is used as a unit of fragmentation(separation) when further fragmentation is required in the RS 20.

The FSN management table storage unit 105, as with the FSN managementtable storage unit 203 in the RS 20 previously described, is used tomanage in the form of table data (an FSN management table) an FSN (NextFSN) that is next added to a SDU, according to the connection identifier(CID) belonging to a PDU to be transmitted. Note that the “Next FSN” isupdated by being increased by 1 each time an FSN is added to a SDU.

The transmission controller 106 has the same function as thetransmission controller 204 in the RS 20 previously described. That isto say, the transmission controller 106 has the function of extracting apacket from the PDU buffer 103 at the PDU transmission timing andtransferring it to the PDU generator 104. The PDU transmission timing,as with the first embodiment, is decided, for example, by a scheduler(not illustrated) of the BS 10 so that QoS (Quality of Service) isguaranteed.

The transmission controller 106 is also adapted to trigger the PDUgenerator 104 with respect to transmission of PDUs, and has a functionof specifying a transmittable PDU length or number of bytes. As with thefirst embodiment, a data quantity, such as a PDU length or number ofbytes, which is transmittable can be decided based on available radioresources (the number of subchannels, number of symbols, and such), andon the modulation method and encoding rate being used. Therefore, insystems adopting adaptive coding modulation, a data quantity, such as aPDU length or number of bytes, which is transmittable can also beadaptively decided based on feedback information on the radio receptionquality from the MS 30 such as CQI, CINR, or the like.

The encoder 107 is used to add to the PDU from the PDU generator 104 therequired error correction codes such as turbo codes etc. The modulator108 is used to modulate the coded data from the encoder 107 using therequired modulation method such as QPSK, 16QAM, or the like. Thetransmitter 109 is used to perform on the modulated signal from themodulator 108 the required wireless transmission process that includesDA conversion, frequency conversion to radio frequency (RF)(up-conversion), amplification to the required transmitting power by ahigh-output amplifier, and so forth.

The duplexer 110 is used to separate an outgoing signal and an incomingsignal, and is adapted to output the outgoing signal from thetransmitter 109 to the transmitter-receiver antenna 111, and output theincoming signal from the transmitter-receiver antenna 111 to thereceiver 112.

The transmitter-receiver antenna (also sometimes simply called anantenna herein after) 111 is used to radiate the outgoing signal fromthe duplexer 110 into space toward the MS 30 or RS 20, and receive asignal radiated into space from the MS 30 or RS 20.

Thus, the above-mentioned encoder 107, modulator 108, transmitter 109,duplexer 110, and antenna 111 as a whole function as packet transmittingunit for transmitting to the RS 20 the PDU that has been generated inthe PDU generator 104 by packing the aforementioned fragmented SDUsafter adding an FSN to each of the SDUs.

On the other hand, the receiver 112 is used for performing the requiredwireless reception process, which includes amplification by a low noiseamplifier, frequency conversion to base band frequency(down-conversion), AD conversion, etc., on an incoming signal that isreceived by the antenna 111 and input from the duplexer 110. Thedemodulator 113 is used for demodulating the incoming signal, on whichthe aforementioned wireless reception process has been performed in thereceiver 112, by a demodulation method that corresponds to themodulation method at the sending side (MS 30 or RS 20).

The decoder 114 is used to decode the incoming signal demodulated in thedemodulator 113, by a decoding method and decoding rate that correspondto the encoding method and encoding rate at the aforementioned sendingside. The SDU regenerator 115 has a function of identifying informationon QoS from the decoded data sent from the decoder 115, for example fromthe CID added to the GMH of the PDU, and regenerating an IP packet etc.according to that information. Note that the SDU regenerator 115 canalso have a function of computing a cyclic redundancy check (CRC) overthe aforementioned decoded data. When an error is detected from thecomputation result, it is also possible for the transmission controller106 to perform retransmission control such as HARQ etc.

(Detailed Description of PDU Generator 104)

The configuration of the above-mentioned PDU generator 104 isillustrated in FIG. 7 by way of example. As illustrated in the figure,the PDU generator 104, in order to implement the functions previouslydescribed, includes a fragmentation/packing determiner 141, an SDUfragmenting unit 142, an FSN/FC assigner 143, an SDU buffer 144, and anFSN assigner 145.

The fragmentation/packing determiner 141 is used to determine whetherthe packet from the packet buffer 103 is fragmented, or transmitted as apacked PDU. The fragmentation/packing determiner 141 is adapted totransfer the packet to the FSN/FC assigner 143 if fragmentation isunnecessary and to the SDU fragmenting unit 142 if fragmentation isnecessary. As to the determination of whether to fragment, for example,if the length of a packet exceeds a predetermined threshold value it canbe determined that fragmentation is necessary, and in the case otherthan that, it can be determined that fragmentation is unnecessary. Thethreshold value may be a preset value, or a value informed by the RS 20.As to the packing, a plurality of packets (including fragmented SDUs)are packed within the range of a transmittable data quantity specifiedby the transmission controller 106.

The SDU fragmenting unit (packet fragmenting unit) 142 is used tofragment an SDU by using the above-mentioned threshold value as areference, and transfer the fragmented SDUs to the FSN/FC assigner 143.The FSN/FC assigner 143 is used to generate and add to the fragmentedSDU or nonfragmented SDU a subheader that contains the corresponding FCand an FSN that is incremented one by one in a series of fragmentedSDUs. The SDU within the range of the transmittable data quantity istransferred to the header assigner 145, while the SDU outside the rangeis temporarily held in the SDU buffer 144 and waits until the nextassignment of a transmittable data quantity.

The header assigner 145 is used to pack one SDU or a plurality of SDUsand add a header (GMH) to generate a PDU, and transfer the PDU to theencoder 107. Note that the SDUs that can be packed are only SDUsbelonging to the same connection identifier (CID).

Thus, the FSN/FC assigner 143, in cooperation with the FSN managementtable storage unit 105 and transmission controller 106, functions ascontroller for adding to each of the fragmented SDUs an FSN which isidentification information, while the header assigner 145 functions aspacket packing unit for packing the fragmented SDUs to which the FSNshave been added.

(Description of Operation of BS 10)

The operation of the BS 10 of this embodiment configured as describedabove will be described in detail herein after with reference to aflowchart illustrated in FIG. 10.

In the BS 10, the transmission controller 106 checks whether atransmission data quantity D has been assigned (i.e., whether the packetfragmenting/packing function has been effectively set) (route N of stepS11). If it has been assigned, a packet to be transmitted is read outfrom the PDU buffer 103 at the aforementioned PDU transmission timing,and is transferred to the PDU generator 104 (route Y of step S11 to StepS12).

In the PDU generator 104, on receiving a packet from the packet buffer103, the fragmentation/packing determiner 141 determines whether thepacket (SDU) is fragmented, or transmitted as a packed PDU. That is, forinstance, by comparing the packet length of the packet with thethreshold value, if the packet length is above the threshold value it isdetermined that fragmentation is necessary, and in the case other thanthat, it is determined that fragmentation is unnecessary.

If fragmentation is unnecessary, the fragmentation/packing determiner141 transfers the SDU to the FSN/FC assigner 143. If fragmentation isnecessary, the fragmentation/packing determiner 141 transfers the SDU tothe SDU fragmenting unit 142. The SDU fragmenting unit 142 fragments theSDU transferred from the fragmentation/packing determiner 141 intoblocks that have a predetermined data quantity X (X<D) (step S13), andtransfers the blocks to the FSN/FC assigner 143.

The FSN/FC assigner 143 generates and adds a subheader, which containsthe corresponding FC, sequence number FSN, and the SDU length (blocklength), to the fragmented SDU from the SDU fragmenting unit 142 ornonfragmented SDU from the fragmentation/packing determiner 141 (stepS14). The FSN/FC assigner 143 transfers to the header assigner 145 theSDU that is within the range of the transmittable data quantity D. TheSDU which is outside the range of the data quantity D is temporarilyheld in the SDU buffer 144 and caused to wait until the next assignmentof a transmittable data quantity.

The header assigner 145 packs a SDU or a plurality of SDUs transferredfrom the FSN/FC assigner 143 or SDU buffer 144 and adds a GMH to it togenerate a PDU. More specifically, for example, if the length of theheader GMH is represented by H and the length of the subheader by SH, nblocks (SDUs) satisfying H+(SH+X)×n≦D<H+(SH+X)×(n+1) are packed andassigned a GMH, whereby a PDU is generated (step S15).

The generated PDU is passed through the encoder 107, modulator 108, andtransmitter 109, and is transmitted to the RS 20 or MS 30 through theantenna 111.

Note that a signal received by the antenna 111 is passed through theduplexer 110, receiver 112, demodulator 113, decoder 114, and SDUregenerator 115, whereby the received signal undergoes the requiredwireless reception process, demodulation process, decoding process,CRC-computation process, etc., and is then transferred to the NWinterface 101.

Thus, the BS 10 fragments a SDU beforehand, adds an FSN to each of thefragmented SDUs, then packs them, and transmits a packed PDU to the RS20. Therefore, in the RS 20, in the case where further fragmentation ofa SDU is necessary, if the SDU is separated into the blocks fragmentedin the BS 10, then the addition of FSNs in the RS 20 (FSN management inthe RS 20) can be made unnecessary. The RS 20 will herein after bedescribed in detail.

(Description of RS 20)

FIG. 8 is a block diagram illustrating a specific configuration in whichattention is directed to the major functions of the RS 20 in thisembodiment. Since the above-mentioned fragmentation of an SDU, additionof FSN/FC, and packing of SDUs are performed in the BS 10, the RS 20illustrated in FIG. 8 differs from the configuration of the RS 20described in FIG. 1 in that the FSN management table storage unit 203 isunnecessary and the PDU reconstructor 202 is replaced with a PDUreconstructor 214. Note that in FIG. 8 and the following description,parts given the same reference numerals as the aforementioned referencenumerals denote the same parts as the aforementioned parts orcorresponding parts, unless otherwise specified.

For the PDU transmitted after undergoing the aforementionedfragmentation of an SDU, addition of FSN/FC, and packing of SDUs, or thePDU transmitted without undergoing these processes, the PDUreconstructor 214 is used to determine whether to fragment the PDUtransferred from a PDU buffer 201 through a receiver 210, a demodulator211, a decoder 212, and through a PDU receiver 213. If fragmentation isnecessary, the PDU reconstructor 214 is adapted to fragment the PDU byseparating the PDU into the blocks (SDUs) that have been fragmented inthe BS 10.

(Detailed Description of PDU Reconstructor 214)

For that purpose, for example, as illustrated in FIG. 9, the PDUreconstructor 214 of this embodiment includes, as its major functions, aPDU length determiner 221, an SDU extractor 226, a packed-SDUfragmenting unit 227, a header assigner 228, and a selector 229.

The PDU length determiner 221, on receiving an MAC-PDU from the PDUbuffer 201 at the aforementioned PDU transmission timing, determineswhether the MAC-PDU is transmittable without being fragmented, based onthe data quantity, such as a PDU length or number of bytes, which istransmittable, specified by the transmission controller 204. If the PDUis transmittable (fragmentation unnecessary), it is transferred to theselector 229, and if it is not transmittable (fragmentation necessary)it is transferred to the SDU extractor 226.

The SDU extractor 226 is used to separate the PDU, which was judged tobe “Fragmentation Necessary” and transferred from the PDU lengthdeterminer 221, into the header (GMH) and the SDU (including thesubheader) stored in the payload, transfer the SDU (including thesubheader) to the packed-SDU fragmenting unit 227, and transfer theheader (GMH) to the header assigner 228.

The packed-SDU fragmenting unit 227, taking the addition of the headerin the header assigner 228 into account, separates the packed SDU intothe SDUs so that each SDU is less than the data quantity specified bythe transmission controller 204. The separated SDUs are transferred tothe header assigner 228, which in turn adds the header (GMH) to each ofthe separated SDUs to generate (reconstruct) a plurality of PDUs. Notethat the PDU not transmittable is transferred to the PDU buffer 201, inwhich it is temporarily held and waits until the next transmissiontiming.

The selector 229, under control of the transmission controller 204, isadapted to selectively transfer the PDU which has been judged to be“Fragmentation Unnecessary” and transferred by the PDU length determiner221, and the PDU which has been transferred from the header assigner228, to the encoder 205. Note that in transferring the PDU to theencoder 205, a CRC code can also be added thereto.

(Description of Operation of RS 20)

The operation of the RS 20 of this embodiment configured as describedabove will be described in detail herein after with reference to aflowchart illustrated in FIG. 11.

In the RS 20, the transmission controller 204 checks whether atransmission data quantity D has been assigned (i.e., whether the packetfragmenting function has been effectively set) (route N of step S21). Ifit has been assigned, a PDU to be transmitted is read out from the PDUbuffer 201 at the aforementioned PDU transmission timing, and istransferred to the PDU reconstructor 214 (route Y of step S21 to StepS22). In the PDU reconstructor 214, on receiving the PDU from the PDUbuffer 201, the PDU length determiner 221 determines, based on thespecified data quantity D from the transmission controller 204, whetherthe PDU is transmittable without being fragmented (step S23).

As a result, if it is not transmittable (i.e., if fragmentation isnecessary) (route N of step S23), the PDU length determiner 221transfers the PDU to the SDU extractor 226. The SDU extractor 226separates the PDU into the header (GMH) (where H is the size of theheader) and the SDU stored in the payload, and transfers the SDU to thepacked-SDU fragmenting unit 227 and the header to the header assigner228.

The packed-SDU fragmenting unit 227 separates the packed SDU from theSDU extractor 226 into the first n SDUs [which satisfyH+(SH+X)×n≦D<H+(SH+X)×(n+1) where H is the header length of the headerGMH, SH is the length of the subheader, and X is the predetermined dataquantity (X<D)] and the remaining SDUs (step S25), and transfers them tothe header assigner 228.

The header assigner 228 adds the header (GMH) to each of the SDUstransferred from the packed-SDU fragmenting unit 227 to generate a firstPDU #1 and a second PDU #2 (step S26). The second PDU #2 is temporarilyheld in the PDU buffer 201 until the next transmission timing, while thefirst PDU #1 is output to the selector 229 to make preparations fortransmission (step S27).

On the other hand, when it is determined in step S23 that fragmentationis unnecessary, the PDU length determiner 221 outputs to the selector229 the PDU transferred from the PDU buffer 201 (route Y of step S23)

The PDU selected in the selector 229 is transferred to the encoder 205,undergoes the required encoding process, modulation process, andwireless transmission process by being passed through the modulator 206and transmitter 207, and is then transmitted from the antenna 209 viathe duplexer 208 (step S28).

As with the first embodiment, a signal received by the antenna 209undergoes the required wireless reception process, demodulation process,decoding process, CRC-computation process, and other processes bypassing through the duplexer 208, receiver 210, demodulator 211, decoder212, and PDU receiver 213, and is temporarily held in the PDU buffer 201until the transmission timing that is specified by the transmissioncontroller 204.

Thus, according to this embodiment, in the BS 10 which is a packetsending station, a PDU that is transmitted is previously fragmented intoSDUs (blocks) which are used as a unit of fragmentation that is usedwhen fragmentation is needed in the RS 20, and the SDUs are packed asone PDU after the addition of an FSN and an FC to each of them, and thePDU is transferred to the RS 20. Therefore, in the RS 20, FSNs and FCsdo not need to be managed as are done in the first embodiment, and byjust separating a packed PDU into the SDUs fragmented in the BS 10, itbecomes possible to fragment and transmit a packet to the MS 30 withoutthe aforementioned FSN conflict and FC mismatch taking place.

Thus, with a malfunction due to the FSN conflict and FC mismatch in theMS 30 being prevented, it becomes possible for the RS 20 to fragment andrelay a received packet according to radio resources such as radio bandsavailable between the RS 20 and the BS 30. Consequently, the utilizationof radio resources becomes possible.

Particularly, in the above embodiment, a header (GMH) is added after thepacking of SDUs, so the header can be greatly reduced compared with thecase where a header is added to each fragment (SDU). Thus, furtherutilization of radio resources is possible.

[D] Others

In the above embodiments, the QoS class of a PDU may be employed as areference of whether to fragment. For example, for a PDU whose QoS classis higher than a predetermined reference QoS, instead of fragmenting thePDU and transmitting the remaining part at the next transmission timing,a request for the required radio resources may be made to thetransmission controller so that transmission can be performed withoutfragmentation.

In addition, it may be determined that the fragmentation of a PDU whosepayload is encrypted is unnecessary. That is, there are cases where ifan encrypted PDU is fragmented without decoding, it cannot be normallydecoded at the receiving side. To prevent this, when radio resources canbe sufficiently ensured, or when a request for sufficient radioresources is sent to the transmission controller, an encrypted PDU canbe transmitted without being fragmented. The presence or absence ofencrypted payload can be identified by using identification bits addedto the header (which is not encrypted).

Finally, the size of fragmentation may be fixed or variable. Thefragmentation size may also be based on the maximum rate between the RS20 and the MS 30 or a smaller rate than that. However, when it is basedon the smaller rate, it is preferable to perform retransmission controlsuch as HARQ etc. at the same time.

INDUSTRIAL APPLICABILITY

As has been described hereinabove, the present invention is capable ofpreventing the FSN conflict and FC mismatch resulting from furtherpacket fragmentation in RS, so flexible packet fragmentation and relaybecomes possible according to radio resources available between RS andMS, and radio resources can be fully utilized. Thus, the presentinvention is considered extremely useful in the field of wirelesscommunication technology.

The invention claimed is:
 1. A relay station for receiving a packettransmitted from a sending station and relaying said packet to areceiving station, the relay station comprising: a packet receiverconfigured to receive a packet fragmented in said sending station; apacket fragmenting unit configured to selectively further refragmentsaid packet received by said packet receiver into a plurality ofrefragmented packets; a controller configured to add a sequence numberto each of said refragmented packets and to a packet not refragmented insaid packet fragmenting unit; and a packet transmitting unit configuredto transmit to said receiving station each of said packets to which saidsequence number has been added by said controller, wherein the sequencenumber is incremented by one independently for each of connections everytime the sequence number is added to each of said refragmented packetsand to said packet not refragmented in said packet fragmenting unit,each of the connections being associated with at least one of adestination of the packet and a QoS (Quality of Service) class of thepacket, wherein the packet fragmenting unit does not refragment saidreceived packet when the QoS class of said received packet is higherthan a predetermined reference QoS or payload of said received packet isencrypted.
 2. The relay station as set forth in claim 1, wherein saidpacket fragmenting unit comprises a fragmentation determiner that, basedon a predetermined reference, determining whether said packet receivedby said packet receiver is further fragmented into said plurality ofrefragmented packets, and a packet refragmenting unit that refragmentssaid fragmented packet if said fragmentation determiner determines thatsaid fragmented packet is further fragmented.
 3. The relay station asset forth in claim 2, wherein if a packet size of said fragmented packetreceived by said packet receiver exceeds a size that is transmittable tosaid receiving station at that time, said fragmentation determinerdetermines that said fragmented packet is further fragmented.
 4. Therelay station as set forth in claim 1, wherein said controller adds saidsequence number to said refragmented packets and said non-refragmentedpacket regardless of said refragmentation.
 5. The relay station as setforth in claim 4, wherein said controller further comprises a sequencenumber manager that manages said sequence number according to aconnection with said receiving station, and said controller adds saidsequence number to said refragmented packet and non-refragmented packetof the same connection under management of said sequence number manager.6. The relay station as set forth in claim 1, wherein there is noconflict among the sequence numbers added by said controller.
 7. A relaymethod for use in a relay station that receives a packet transmittedfrom a sending station and relays said packet to a receiving station,the relay method comprising: receiving a packet fragmented in saidsending station; selectively further fragmenting said fragmented packetinto a plurality of refragmented packets; adding a sequence number toeach of the refragmented packets and to a non-refragmented packet notfragmented; and transmitting to said receiving station each of saidpackets to which said sequence number has been added, wherein thesequence number is incremented by one independently for each ofconnections every time the sequence number is added to each of therefragmented packets and to the non-refragmented packet not fragmented,each of the connections being associated with at least one of adestination of the packet and a QoS (Quality of Service) class of thepacket, wherein said fragmented packet is not further fragmented whenthe QoS class of said fragmented packet is higher than a predeterminedreference QoS or payload of said fragmented packet is encrypted.
 8. Therelay method as set forth in claim 7, wherein there is no conflict amongthe sequence numbers.